The present invention relates to apparatus for highly precise manufacture of individual cured elastomeric piece parts, such as fluid seals, and by way of example, to the manufacture of half seal units adapted to be placed together in an assembled relation for use as an annular shaft seal and characterized by the presence of a metal or other reinforcing stiffener therein.
Although molded products such as the half seal units of the type able to be manufactured by the techniques of the invention have a superficial appearance of simplicity, these units must be made at low cost under extremely precise conditions of manufacture. This is because, although the unit price of the piece parts is low, they are customarily installed in extremely inaccessible locations wherein replacement in the event of leakage would involve the expenditure of a great deal of labor. Because of extrinsic factors, such as the construction of associated parts with which the seals are to be used, such seals are commonly manufactured as half seal units for subsequent assembly. Typically, the complete seal units are used in automobile and truck engines as a rear main bearing seals, and therefore form a sealing fit with a reduced diameter section of the crankshaft lying behind the rear main bearing surface and ahead of an enlarged diameter flange to which the flywheel is secured. Since there is no axial access to this area, the seals are installed by halves, usually just prior to installation of the bearing caps. These units are expected to last for the anticipated lifetime of the engine and must resist physical and chemical attack, high peripheral speed and the like. Normally, therefore, such seals are made from synthetic elastomers such as silicone rubbers.
In view of the inaccessibility of the seal after installation, manufacturers of automobile engines and other components using these seals subject the finished half seals to a rigorous pre-installation inspection program, and the standards required of acceptable seals include freedom from voids or pock marks, absence of flash on most or all surfaces, very accurate radial and axial dimensional control, proper insert positioning, flatness of opposed edge portions which form the split line, and freedom from puckering or buckling during installation and use. The interest of the manufacturer in providing fully reliable seals is heightened by warranty obligations which are quite common and by a general interest in the quality image created by oil-tight assemblies.
Furthermore, known injection molds have not been satisfactory to provide high quality parts such as those required in certain original equipment oil seal applications, such parts having previously been characterized by unevenness, distortion of inserts, the presence of knit lines and flash, and other drawbacks which have characterized attempts to mold rubber products along the lines previously used in the manufacture of non-precision thermoplastic products.
In view of the foregoing disadvantages of prior art methods and apparatus, it is an object of the present invention to provide one or more suitable apparatus for making improved precision molded products.
A further object is to provide molding apparatus capable of producing finished parts having a minimum of flash and having whatever flash may be produced confined to particular, predetermined locations.
Another object is to provide molding apparatus wherein a single force press system may be used to provide for mold clamping and part removal along two different axes.
A further object is to provide a molding apparatus providing for positive stripping and removal of a finished part having undercut surfaces and the like without bringing about damage to the finished parts.
Another object is to provide a molding apparatus characterized by particular locations of flash gates and elimination of the necessity to register the top and bottom mold plates to obtain accurately formed parts.
A further object is to provide an apparatus suitable for multiple injection molding of half seals and like parts in a symmetrical half seal design.
A further object is to provide in one embodiment of the invention, a mold having single axis movement and including a mechanically operated stripper plate for cooperative use with a self centering stripper core.
Another object is to provide a molding apparatus characterized by balanced in flow of the fluent elastomer prior to curing thereof.
A still further object is to provide molds which, upon part removal, eliminate the application of tearing stresses to critical areas.
Another object is to provide a molding apparatus wherein so-called knit lines, voids, flash, and other undesirable finished product features may be avoided or minimized.
A still further object is to provide a mold construction which is compatible with existing equipment utilizing vertical movements for preliminary closure, closure during injection, and rubber injection, all on a common axis.
It is a further object of the invention to provide a molding apparatus for use in precision manufacture of parts having an elastomeric component wherein opening the apparatus for part removal inherently simultaneously supports the part against movement and operates to tear the web of elastomeric material between the sprue and the part at a precisely determined point.
Another object is to provide a molding apparatus including a mold unit which is vented, such as to a vacuum source, so as to permit relatively low cavity pressures, thereby helping to evacuate gases formed during molding and lowering injection pressures so as to minimize or eliminate flash formation.
A further object is to provide molding apparatus wherein means are provided for receiving any overflow of elastomer necessary to provide complete mold filling and to provide this feature in an arrangement having means to prevent mold clogging.
These and other objects and advantages of the invention, including certain inherent objects and advantages thereof, are achieved by providing, on the one hand, a molding apparatus having at least one molding cavity defined at least partially by mold sections adapted to move axially for stripping the piece parts from the cavity and having means associated with these sections for ejecting finished, molded parts transversely to the axis of mold opening by subsequently actuable ejectors adapted for cooperation with the strippers in the opened position of the mold, and on the other hand, by a mold unit having a center inlet and means for drawing the injected elastomer toward opposite end face surfaces, and wherein a first vertical mold opening movement sequence partially strips the part from the mold cavity and further stripping is accomplished by subsequent movement of a lower mold portion, leaving the finished part suspended between separated upper and lower mold parts.
The manner in which the invention achieves these objects and advantages, and others, may be best understood when reference is made to the following detailed description of the preferred embodiments of the invention, set forth by way of illustration, and when reference is made to the accompanying drawings, wherein like reference numerals indicate corresponding parts throughout.